1. Field of the Invention
This invention relates to an improvement on a system comprising a camera which is arranged to measure and integrate an incident flash light coming through a photo-taking lens either directly or through a reflection light thereof, that is, to be capable of performing the so-called TTL flash control action, and a flash device which is arranged to be mounted on the camera.
2. Description of the Related Art
The conventional TTL flash control method has been as follows: for example, a light measuring sensor disposed within a camera body is arranged to capture the reflection on the surface of a film or a shutter curtain of flash light of a flash device coming through a photo-taking lens of the camera. The reflection light is integrated and checked for a given quantity of light. Upon detection of attainment of the given quantity of integrated light, a flash stopping signal is sent out from the camera body to the flash device. The signal causes the flashing action of the flash device to be brought to a stop by means of a commutation circuit or the like.
The above-stated given quantity of light is determined by an unconditional computing operation on the sensitivity of a film in use, an aperture value selected, a synchronizing shutter speed, etc. The method gives an excellent result for a certain object, such as a gray reflection plate of a reflection factor of 18% or the like. However, it often fails to have a white or black object photographed in a white or black color. Therefore, for a reversal film which is difficult to do corrective printing, the method has been hardly satisfactory.
It has been another shortcoming of the conventional method that an intrinsic automatic operating function of the flash device cannot be utilized when the photographer manually allows the flash device to flash by manually selecting an aperture value.
To solve these problems, a system has been proposed, as disclosed in Japanese Laid-Open Patent Application No. SHO 61-156238. The system is arranged to preliminarily allow the flash device to flash; to measure the light within the camera body; to allow the TTL flash control to perform after the result of the preliminary light measurement is corrected by the photographer as desired. However, this system necessitates many steps of operation and, therefore, is not suitable for continuous photographing. Besides, the cost of it increases because of many additional circuit required.
In a conceivable method for eliminating the above-stated shortcomings, a correction value indicating a variable degree of flash control level is set independently of an exposure level determined according to the normal light. That method enables the intention of the photographer to be reflected on the result of control. However, the method has the following shortcomings:
It complicates the operation on the camera for the photographer who does not require such a correction value. If the photographer does not understand the meaning of flash control correction, it might incur a failure. Besides, if the correction setting member is arranged to be easily movable, a correction value might be accidentally set without the photographer's knowledge, for example, while the camera is carried. Further, a photographing operation might inadvertently be performed with the camera system left at a previously set correction value when the correction value must be reset.
Further, with a flash device arranged to permit the above-stated correction value to be set thereon, the camera system should be arranged to have information on the set correction value transmitted from the flash device to the camera body and to allow a control circuit on the side of the camera body to control the quantity of light accordingly. In this instance, however, if the camera on which the flash device is to be mounted is not provided with this control circuit, the light quantity control cannot be accomplished according to the flash control correction value set on the side of the flash device. The photographer might be confused on that occasion.